1. Field of the Invention
This invention relates to a safety belt wind-up device for automatically winding up a safety belt or band for vehicles such as automobiles, and more particularly to a safety belt wind-up device including means for locking a wind-up force or tensile force.
Various kinds of wind-up devices have been suggested. One of the most common devices comprises a coil spring for producing a wind-up force of a wind-up shaft. With this device, the longer or further the belt is drawn out of the device, the greater the belt wind-up force becomes as a result of the coil spring being squeezed. The increased wind-up force is therefore transmitted through the belt to a user, equipped with the belt of the device of this type, who is directly subjected to the wind-up force.
Another device hitherto suggested comprises means for controlling the wind-up force of a coil spring depending upon the length of a drawn belt to overcome the above disadvantage. However, the wind-up force acting upon the belt in such an equipped condition is not deleted but only mitigated, so that a user is subjected to a compressive force which is uncomfortable for him. Moreover, as the wind-up force is controlled depending upon the length of the drawn belt, the wind-up force acting upon the belt varies with the length of the drawn belt, so that users are subjected to compressive forces different according to their physique.
Further wind-up devices hitherto suggested comprise wind-up force lock means to avoid a compressive force acting upon a user equipped with a safety belt of the device. Some of the devices do not allow users equipped with the belts to move to determined extents and when they returned to the original seat position the devices lock the wind-up force in the extended condition without winding up the belts. Other devices allow users to move only within very short distances (for example, corresponding to one revolution of a reel), even if the devices comprise wind-up force lock means for locking original wind-up forces. Therefore, if the users move beyond the short distances, the positions of the equipped belts are shifted when they return to the original seat positions so that the loosened belts are locked, which would not perform their function as safety belts. In order to avoid this disadvantage, an over drawn belt cancelling switch is provided on a buckle to detect the originally equipped position of the belt and thereafter the wind-up force is locked. Such an operation is very troublesome. Furthermore, with other devices after wind-up forces have been locked if the belts are intentionally drawn and released, the belts are returned to locked positions by main springs, at which moments the lock means are apt to be damaged. In addition, with other devices solenoids used in wind-up force lock means are not sufficiently protected, so that dust and salt water enter the devices to cause electrical troubles of the solenoids resulting in malfunctions.